|Abstract:||This paper presents an Incentive-based Sharing (iShare) protocol that blends cellular and ad hoc networks for content dissemination services. With iShare, mobile users download content from a source via cellular links and at the same time form a mesh ad hoc network for peer-to-peer exchange of content data. The mesh remains robust to network dynamics, minimizes ad hoc communication overhead, and parallelizes the downloading process among mesh members. In order to counter selfish behavior, we apply an efficient and practical "tit-for-tat" incentive mechanism, which exploits proximity and mutual content interest of mobile users. This mechanism becomes particularly effective in the case of network dynamics since we utilize promiscuous and broadcast modes of the ad hoc channel. As a result, our protocol effectively helps to free resources in the cellular network and accelerates the content download for its users. Furthermore, it enables users to continuously obtain data via ad hoc connections during cellular handoff periods and provides multi-homing downloads for groups spanning adjacent cells. We evaluate the performance of iShare by means of simulations and compare it to other content dissemination schemes using cellular broadcast channels, cellular unicast channels, and tree-based protocols. The obtained results show that iShare significantly outperforms alternative approaches and creates a win-win situation by improving performance of both iShare and other mobile users.